Process for conducting partial oxidation of hydrocarbons



PROCESS FOR CONDUCTING PARTIAL OXIDATION OF HYDROCARBONS United States 2,810,739 Patented Oct. 22, 1957 PROCESS FOR CONDUCTENG PARTIAL QXIDATIN 0F HYDRCARBNS William C. Lake, Tulsa, Okla., and George M. Bamboe is, St. Paul, Minn., assignors to Pan American Petroleum Corporation, a corporation of Delaware Application March 15, 1954, Seriai No. @6,361

12 Claims. (Cl. 26d-449.6)

Our invention relates to a novel method for conducting the partial oxidation of hydrocarbons. More particularly, it is concerned with a procedure for quenching the products from a hydrocarbon oxidation process by the use of a fluidized bed of hydrocarbon synthesis catalyst While employing the latter in hydrocarbon synthesis.

In the partial oxidation of hydrocarbons, such reaction is usually conducted in the vapor phase, streams of oxygen-containing gas and hydrocarbon being separately preheated up to or slightly below the threshold temperature of the reaction prior tothe introduction of said gases into a suitable reaction zone. The reaction itself becomes highly exothermic once the critical temperature required to initiate the oxidation has been reached and, accordingly, it is generally necessary to limit the extent of conversion (by controlling the amount of oxygen in the reaction mixture) in order to maintain the temperature within the reaction zone at the aforesaid critical level. Once the desired oxidation products are formed, they should be withdrawn from the reaction zone as rapidly as possible because of their tendency to decompose into less desirable products on continued exposure to high temperatures. This object is generally acomplished by the use of a quenching step, i. e., the supplying of conditions which lower the temperature of the oxidation products to a level at which they are stable. In the past, the principal quenching agent for this purpose has been water or dilute aqueous solutions of certain chemicals derived from various separation stages of the product processing operation. While these methods served to bring the temperature of the product chemicals down to a level at which such chemicals were stable, the latter were obtained in extremely dilute solutions, e. g., l to 5 percent, thereby necessitating expensive processing steps and relatively large-sized equipment to accomplish satisfactory concentration and purification of said chemicals.

We have now discovered that the foregoing and other disadvantages may be readily overcome by employing a fluidized bed of a finely divided hydrocarbon synthesis catalyst as a quenching medium for the hot gaseous products resulting from the partial oxidation of hydrocarbons, such as, for example, propane, butane, etc. This result can be accomplished by such means since the temperature of the fluidized bed of hydrocarbon synthesis catalyst is generally in the neighborhood of from about 600 to 650 F., while the temperature of the exit gases from the partial oxidation zone may range from about 750 to about l000 F. rhe large surface area available in the bed serves as a heat transfer medium .to remove the heat of reaction and as an inhibitor to halt further om'dation by deactivating the active molecular fragments on the surface of the catalyst. As previously pointed out, the oxidation of hydrocarbons is a highly exothermic reaction characterized by an induction period of relatively slow rate followed by a more rapid autocatalytic chain propagated reaction. Deactivation of the activated molecules and consequent stoppage of the reaction is accomplished by collision with a surface. However, no appreciable decline in reaction rate can be accomplished by wall surface alone. Thus, the need for a large surface area to halt the reaction at the desired stage and to remove heat from the system. Since many of the chemicals formed by the partial oxidation of hydrocarbons are unstable at the ternperatures required for the reaction itself, cooling to quench the reaction products is accomplished by the process of our invention generally by maintaining the temperature of the fluidized bed in the hydrocarbon synthesis Zone sufficiently below the temperature of the partial oxidation zone. The amount of heat usually desired to be removed from the oxidation products entering the synthesis reactor is relatively slight compared to the heat accompanying the synthesis reaction, since the oxidation products ordinarily constitute only a small porportion of the total feed and only sensible heat needs to be absorbed. T he oxidation product stream is cooled from a temperature of, for example, from about l000 F. down to about 650 F., by introducing recycle and fresh feed into the synthesis reactor at temperatures of 30 to 40 F. lower than is normally done, i. e., 300 to 400 F. Gr, if desired, the use of lower preheat temperatures for the oxidation reaction tends to reduce considerably the temperature of the oxidation products. Actually, a substantial quenching elect can be realized even if no appreciable difference exists between the temperature of the fiuidized bed and that of the aforesaid hot gaseous reaction products where relatively low concentrations of oxygen, i. e., not more than about 3 percent, are employed in the oxidation reaction mixture, owing to the surface eect alone, as provided by the conditions of our invention. However, higher oxygen concentrations may be employed in instances Where a reactor is used having a relatively low length-to-diameter ratio, such as described in copending application, U. S. Serial Number 358,641, tiled Iune l, 1953, by J. W. Palm. With reactors of this type, the feed may, for example, in the case of butane, be injected at a relatively low temperature, i. e., 325 to 350 F., the allowable quantity of oxygen in such feeds varying indirectly with the temperature. For example, at a preheat level of 325 to 350 F., the feed to the oxidation reactor may contain from about l2 to about 13 percent oxygen. Under such conditions, the cool feed is thoroughly mixed with hot gaseous reaction products, thus eliminating any necessity for removal of heat from the reactor. Gaseous partial oxidation products produced in a reactor of this type may be, as they leave the reactor, at approximately the same temperature as that of the catalyst in the hydrocarbon synthesis Zone, i. e., from about 600 to about 675 F. Partial oxidation products at such temperatures may be satisfactorily quenched by rapid injection into the hydrocarbon synthesis zone solely as a result of the large surface area of the fluidized catalyst with which said products come into contact.

Thus, by operating in the above manner, it is possible to secure close control of the quench temperature with the attendant advantage of large heat transfer properties characteristic of fluidized beds. Also, need for diluents in the reactant streams, as previously required for the purpose of acting as a heat transfer medium and reaction dampener, is eliminated. As a result, the product stream thus obtained is concentrated as much as 100 fold over the product streams obtained by rnethods employing water or similar liquids as the quenching medium. Because the necessity for large quantities of diluents is eliminated by the process of our invention, smaller sized equipment than has been normally used may be employed, thereby providing for more favorable operating costs. Still another advantage of our invention is that the heat transferred in the quenching step of our process is readily and efnciently recoverable in the form of steam, whereas, present practices employed for the quenching operation lead to relatively high heat losses that are not recoverable. `Y In carrying out the process of our invention, hot' gaseous j products from the partial oxidation of hydrocarbons, usually at Va temperature of at least about 750 F., are injected into the reaction zone of a hydrocarbon synthesis .reactor where they are quenched or cooled by contacting .the large surface area afforded by the fluidized catalyst bed `which is generally at a temperature of from about 15,0" to about 400 F. below the temperature of said products These hot gaseous products may be introduced into the reactor independently of or with the synthesis feed.V The partialoxidation reaction .itself may be carried out .in Yaccordance withknown conditions of temperature, pressure, feed composition, linear velocities and the like. Thus, for example, we'may employtemperatures of Vfrom about n800" toabout 1000 F., pressures nranging from about atmospheric Vto about Y500 or 600 Vp. s. i. and a linear velocity of about feet pery second. 'The feed should generally Vbe on the hydrocarbon rich lside'softhat the resulting gases from the oxidation reaction will not disturb the reducing conditions required for the hydrocarbon synthesis reaction.

' Ordinarily, the oxidation products fed to the hydrocarbon synthesis reactorconstitute about 8 or 9 percent `of the total feed, although higher percentages of oxidation products may be employed, e. g., 25 to 30 percent, ex-

cept that when air is used as the oxidizing agent, nitrogen concentrations in the feed usually become objectionable if much more than about 12 to 15 percent of the synthesis total 'feed is derived from the aforesaid hydrocarbon oxidation step. Thus, if the amount of oxidation reactor product gas is increased, Ythe percent air fed to the oxidationreactor should be decreased accordingly in order to keep'the nitrogen content in the product gas at a substantially constanttigure. Y

With'pure .oxygen as the Voxidizing agent, the amount of oxidation products is limitedV by the diluting effect of the 'hydrocarbons being oxidized rather than by the combined effect of nitrogen and the' hydrocarbons which occurs when airis used. VSince the hydrocarbons'being oxidized are present in a concentration.approximately 5 times greater 'than thenormalnitrogen concentration in the Vhydrocarbon synthesis total feed,'rnuch.more hydrocarbon than nitrogen can be tolerated in the synthesis reactor before "the dilution effect becomes appreciable because hydrocarbonsQsuch'as, for example, butane, can be removed `as liquid product in'the recoverysystem and,if desired,

used fasfeedfor the aforesaid oxidation reaction. 'The percent 'oxygen inthe feed to the partial oxidation step vdown to a reasonable level. The percentage of oxidation products in the total feed tothe synthesis reactor should not be allowed to` exceed about to 30 volume percent Vin order to avoid excessive temperatures in the synthesis reactor and to keep Vvthe concentration of oxidation products down to a'level at whichsynthesisreactions are not suppressed.

The process of our invention may be'further illustrated by explanation of the accompanyingflow diagram in which air-and butane are separately preheated to a temperature of'about''650 Ffin preheaters 2 after which the hot air and hydrocarbon are sent through'lines 4 and A6, respectively, to an oxidation reactor 8 which forms the lower portion of a unit 10, the upper partof whichfunctions as a hydrocarbon.synthesis-.zone or reactor 12, Oxidation reactor 8 and synthesisreactor 12 are separated by Ygrid 14, The hotgases in1lines'74 and '6 are mixed in Y proportions such as to give-a fresh feed of the following composition; 171 percent oxygen, 41.3 percent nitrogen, and 47.7 percent hydrocarbon, (butane).` The oxidation `unit is operatedat a pressure-ofabout 400,p.'s. i. Vand aV vshould not be muchin excess Vof 15 to 20 volume percent Y 1n order to keep-the temperature of the oxidation products contact time of about 0.5 second is employed. Product gases issuing from the oxidation reactor have the following approximate composition:

Component: Y Mol percent CO2 0.5 CO 5.0 H2 1.0 N2 40.4 Paraftin hydrocarbons V32.2 Olelins 7.*1 Chemicals 4.9 Water 8.9 Oxygen 0.0

These gases, which arcata temperature of about 950:F., contact the fluidized iron hydrocarbon synthesis catalyst mixed with the fresh feed and recycle streams in synthesis zone 112 and are substantially immediately Vreduced'tofthe temperature of the catalyst,fi. e., 650 F. In thisconnection, the oxidation Vproducts sneed-not be mixed with the Yfreshieed and recycle gases but maybe injectedinto .the hydrocarbon synthesiszone just above Ygrid 14. Synthesis fresh feedis introduced into the system vviafline 15 and has the following composition:

Component:

- CO2 1.8 CO .30.4 H2 V 58.0 N2 2.3 Parafns V`7.5

fThisfeed is mixedjwith recycle gasfin line 16 kin a ratio of about 1:'71 to give a total feed, including partial oxidation products',` having the following composition:

After increasing the temperature of the resultingtotal Vfeed to Vabout'3'50 F. in preheaterll, itis introduced into hydrocarbon synthesis zone 12.

A linear velocity of about 0.6 feet per second risnsed and space velocity of the 'order of about 4 to5 S. C. H. CO (total feed)/#' Fe Vcatalyst uidized is employed. Heat is removed from the synthesis zone ,12 by `means of a suitable heat transfer agent such as, for example, diphenyl, circulating in jacket 3fthrough line i7 where it is introduced into a suitable waste'heat boiler 19 and thereafter the Vcooled material again introduced into the 'reaction jacket via line.21. Product gases from the top of the synthesis 'zonejZ 'are withdrawn through line k18, sent'through condenser 20, and the resultinggaseous-and Vliquid products transferred `to separator 22 where an aqueous'layer containing water and 'water soluble chemicals-iswithdrawn-through linej24. VA product oil phase containing 'chiey hydrocarbons together with somel oil soluble chemicals is'takenroff throug'hline 26, while,un condensed product `gases are sent through Vline 28 to hydrocarbon recovery system` 30. Aportion of ythis stream in line 28, by-passes recovery system 30 and is Vintroduced'into synthesis zone Y12 via line V16, along with 'synthesis freshV feed as indicated above; 'Y The butane fraction; obtainedfrom- `the. hydrocarbon recovery system 'is sent-to oxidationrreaction'fS via lines V32 andf6.in anV amount suticient to maintain a hydrocarbon concentrationin the feedk tosaid'reactor'of. about 45 to '48 percent. 4By" this'means, oncethe process is initiated, 'feredto .oxi- 'dation unit-Sis generated within thesystemfand, hence,

VMol percent the use of butane from an external source is no longer required. If desired, a portion of the stream in line 32, consisting of propylene and heavierhydrocarbons may be withdrawn from the system through line 36. Excess gaseous hydrocarbons are withdrawn through line 34 and used as plant fuel.

The results secured by operating in the above-described manner are noted in the table below. Also, for the sake of comparison, the results obtainable by carrying out, separately, hydrocarbon synthesis and partial oxidation operations under the respective conditions otherwise set forth immediately above are shown in the table below. Por convenience in reporting the results obtained by the process or" the present invention, the latter will be referred 1 Net=total chemicals minus chemicals in feed to synthesis reactor.

Also a comparison may be shown with respect to distribution of oil soluble chemicals produced in ordinary hydrocarbon synthesis and by means of the process of the present invention as follows:

Table II Oil Soluble Product, Distribution Percent- Normal Oxidation- Carbon Atom Basis HCS Synthesis Total 1 36 48 43 33 19 15 2 4 Formals and 1 No oil soluble chemicals in the feed.

As in the case of the results involving water soluble chemicals shown in Table I, it will be seen in Table Il that a relatively large increase in alcohols is experienced by the use of our invention over the quantity of alcohols produced in ordinary hydrocarbon synthesis. Likewise, in the above tables, it is seen that the quantity of alcohols produced in our Oxidation-Synthesis process is substantially greater than would be expected from similar gures for these compounds as produced in normal hydrocarbon synthesis and ordinary partial oxidation procedure. Actually, if the results secured were merely the sum of the results obtainable by ordinary hydrocarbon synthesis and by customary partial oxidation procedures, it would be expected, for example, that the distribution of alcohols produced by the present invention would lie some place between 3l percent for ordinary partial o"idation and 49 percent for normal hydrocarbon synthesis. ln ri`able l, in the column headed TotaL it is indicated that 59 percent of the total chemicals formed by our process are alcohols, and 24 percent are carbonyls.

The table belou.l sets forth still another means of evaluating the process of our invention wherein the results are expressed on the basis of percent selectivity of converted carbon monoxide. Again pointing out the substantial increase in proportion of alcohols which may be secured when operating in accordance with our invention.

it will be apparent from the foregoing discussion that we have provided a procedure for effectively quenching the hot gaseous products resulting from the partial oxidation of hydrocarbons which procedure eliminates a very appreciable portion of the expenses entailed in the recovery of the crude mixtures produced by such partial oxidation process. Likewise, it will be apparent that the process of our invention is also useful in modifying conventional hydrocarbon synthesis operations to secure desired changes in the distribution of both oil and water soluble chemicals produced by said synthesis.

'We claim:

1. In a process for the partial oxidation of hydrocarbons in the vapor phase at a temperature not in excess of about i000L7 F. and under other known conditions to produce a hot gaseous mixture containing valuable oxygenated hydrocarbons, the improvement which comprises contacting said mixture in a reaction zone substantially as soon as said mixture is formed with a uidized bed oi hydrocarbon synthesis catalyst which is in contact with a gaseous mixture containing carbon monoxide and hydrogen in hydrocarbon synthesis proportions under known synthesis conditions, said hot gaseous mixture being introduced into said zone in an amount such that it constitutes no more than about 25 or 30 volume percent of the gaseous mixture in said zone when substantially pure oxygen is used as the oxidizing agent in said partial oxidation process and no more than about l2 to l5 Volume percent when air is used as the oxidizing agent in said partial oxidation process, and allowing said hot gaseous mixture to contact said uidized bed whereby further conversion of said oxygenated hydrocarbons is halted White hydrocarbons and additional oxygenated compounds are being independently synthesized in said zone under said known conditions.

2. ln a process for the partial oxidation of hydrocarbons in the Vapor phase at a temperature not in excess of about l000 F. and under other known conditions to produce a hot gaseous mixture containing valuable oxygenated hydrocarbons, the improvement which comprises contacting said mixture in a reaction zone substantialiy as soon as said mixture is formed with a flui-dized bed of hydrocarbon synthesis catalyst which is in contact with a gaseous mixture containing carbon monoxide and hydrogen in hydrocarbon synthesis proportions under known synthesis conditions, said hot gaseous mixture being at substantially the same temperature as said hydrocarbon synthesis catalyst and constituting not more than about 25 or 30 volume percent of the gaseous mixture in said zone when substantially pure oxygen is used as the oxidizing agent in said partial oxidation process and no more than about l2 to 15 volume percent when air is used as the oxidizing agent in said partial oxidation process, and allowing said hot gaseous mixture to contact said iiuidized bed whereby further conversion of said oxygenated hydrocarbons is halted while hydrocarbons and additional oxygenated compounds are being independently synthesized in Said zone under said known conditions.

3. The process of claim 2 in which said hot gaseous mixture results from the partial oxidation of butane.

4. The process of claim 2 in which said hot gaseous mixture results from the partial oxidation of propane.

5. In a process for the partial oxidation of hydrocarbons in the vapor phasetat a temperature not in ex- ,the improvementV ,which Vcomprises removing the heatV ^-,from said products substantially as-soon `v,as ,they are -formed by. introducing saidtproducts intonai'reaction'zone containing a Vi'lruidizved bed of hydrocarbon synthesis cata- V`lyst whichY is in YContact withta gaseous mixture containing carbon monoxide'and hydrogen in'hydrocarbon Y synthesis proportions ata temperature not in excess of about 650 F. and at other known synthesis conditions, said products -being introduced in an amount such that `they constitute nomore than aboutor 30 volume percent oftheaforesaid gaseous'rnixture when substantially pure oxygen is used as the-oxidizing agent in said partial oxidation process and no more thanabout l2V to 15 vol- `urne percent when air-is used-as the oxidizing agent in 'said partial oxidation process, and allowing said products to Contact slaid=uidized b ed whereby the'temperature of said productsis reduced to thetemperature prevailing within `said -zone while 'hydrocarbons and valuable oxygenated compounds are being independently synthesized insaid zone.

6. The process of claim 3 in which butane -is the 'hydrocarbon subjected to the partial oxidation. 7. Therprocess of claim 3 in which propane isV the 'hydrocarbon subjected to the partial oxidation. Y

}8.^In a process for the synthesis of hydrocarbons and valuable oxygenated-organic compounds by contacting a synthesis total feed mixture containing carbon monoxide -tandthydrogen with a uidized bed of hydrocarbon synthesisA catalyst in a reaction zone at a temperature not inexcess of about 650 E. and atkother known hydrocarbonfsynthesis conditions, the improvement which comprises injecting into 'said zone at a temperature of atV least about 750 YF. hot gaseous products resulting from the partial oxidation of a hydrocarbon at a temperature 'not-infexcess of about l000 F. as soon as said products are formed, said products being introduced in an amount such-that they constitute not more than about 25 or 30 `volume percent of said synthesis total feed mixture when substantially pure oxygen is used as the oxidizing agent in said partial oxidation process and no more thanabout i12 to -l-5volurne percent when air is used as the oxidizing agent in said partial oxidation process, and allowing 'said products to contact said iluidized bed whereby the temperature of said products is reduced to the tempera- 'ture prevailing within said reaction zone While said hyvdrocarbons and valuable oxygenated compounds are being independently synthesized in said zone under said known `conditions.

9. lIn a pro-cess for the synthesis of hydrocarbons and vduableoxygenated organic compounds by contacting a synthesis total feed mixture containing carbon monoxide vrand hydrogen with a uidized bed or".hydrocarbon synthesis-catalyst ina reaction zone under known-hydrocarbon synthesis conditions, the improvement which comprises injecting into said 'zone hot gaseous products resulting from the -partial oxidation of hydrocarbons at a-ternperatur-e not in excess of about 1000" F. as soon as said products are formed, said products being introduced in Yan amount such that they constitute not more -than about 25 or 30 volume percent of the gases in said reaction zone when substantially pure ozygen is used as the Yoxidizing agent in said partial oxidation process and 'no more than about 12 to 15 volume percent when air is used as the oxidizing agent in saidrpartial oxidation process, and allowingsaidhot gaseous products toY contact said uidized bed whereby further conversion of said products is halted while hydrocarbons and addit* 8 Y Y tional oxygenated compounds are being independently synthesizedrinesaidzzone under-said Vknown conditions.

10. "Inaprocess'for the synthesis ofhydrocarbons-and valuable Loxygenated organiccompounds by contacting afsynthesistotalffeedmixture containing carboni monoxide ture in Ysaid zone when-substantially pure oxygen is usedV as the oxidizing agent in fsaidjrpartial oxidation process and no more than about l2 to l5 volume percent when air is used as theoxidizing agent in said partial oxidation process, and-allowing said hot gaseous `rproducts to vcontact said iluidized bedV whereby further conversion of said products is halted While hydrocarbons and additional oxygenated ycompounds are being vindependently synthesized in said zone under said knowntconditions. t ll. ln a process for the partial oxidation Yof hydrocarbons with substantially pure oxygen in the yapor, phase at -aqtemperature not in excess of vabout l000 F. and under other vknown conditions Vto produce a hot gaseous mixture Vcontaining valuable oxygenated hydrocarbons, the improvement which comprises contacting said mixture in a reaction zone substantially as soon as said mix-V ture is formed with a fluidized bed of hydrocarbon synthesis `catalyst which is in contact with a gaseous mixture Y containing carbon monoxide and hydrogen in hydro-l carbon synthesis proportions under known hydrocarbon synthesis conditions, said hot gaseous mixture being introduced into said zone in an amount such that it consrtitutes no-more than about 25 to V30 volume percent t of 'the gaseous mixture in said zone, and allowing said hot gaseous mixture toY contact said Viiuidied bed whereby further conversion of said oxygenated hydrocarbons is halted while hydrocarbons andV additional oxygenated compounds are being independently synthesized in said zone under said known hydrocarbon synthesis conditions.

l2. ln a process for the partial oxidation of hydrocarbons with air in the vapor phase at artemperaturenot in excess of about 1000 F. and under other known conditions to produce ahot gaseous mixture containing valuable oxygenated hydrocarbons,V the improvement which comprises contacting .said mixture 'in a reaction zone substantially as soon as said mixture is formed with a uidized bed of hydrocarbon synthesis catalyst which is in contact with a gaseous mixture containingtcarbon monoxide and hydrogen in hydrocarbon synthesis 'proportions under known hydrocarbon synthesis conditions, said hot gaseous mixture being introduced into said zone in'an'amount such that it constitutes no more than about 12 kto l5 Volume percent of the gaseous mixture in said zone, and allowing said-hot' gaseous mixture to contact said uidized bed wherebyrfurther conversion of said oxygenated hydrocarbons is halted while hydrocarbons and additional oxygenated compounds are being independently synthesized in said zone under said known hydrocarbon synthesis conditions.

References Cited in the le of this patent UNITED STATES PATENT S 

1. IN A PROCESS FOR THE PARTIAL OXIDATION OF HYDROCARBONS IN THE VAPOR PHASE AT A TEMPERATURE NOT INEXCESS OF ABOUT 1000*F. AND UNDER OTHER KNOWN CONDITIONS TO PRODUCE A HOT GASEOUS MIXTURE CONTAINING VALUABLE OXYGENATED HYDROCARBONS. THE IMPROVEMENT WHICH COMPRSES CONTACTING SAID MIXTURE IN A REACTION ZONE SUBSTANTIALLY AS SOON AS SAID MIXTURE IS FORMED WITH A FLUIDIZED BED OF HYDROCARBON SYNTHESIS CATALYST WHICH IS IN CONTACT WITH A GASEOUS MIXTURE CONTAINING CARBON MONOXIDE AND HYDROGEN IN HYDROCARBON SYNTHESIS PROPORTIONS UNDER KNOWN SYNTHESIS CONDITIONS, SAID HOT GASEOUS MIXTURE BEING INTRODUCED INTO SAID ZONE IN AN AMOUNT SUCH THAT IT CONSTITUTES NO MORE THAN ABOUT 25 OR 30 VOLUME PERCENT OF THE GASESOUS MIXTURE IN SAID ZONE WHEN SUBSTANTIALLY PURE OXYGEN IN USED AS THE OXIDIZING AGENT IN SAID PARTIAL OXIDATION PROCESS AND NO MORE THAN ABOUT 12 TO 15 VOLUME PERCENT WHEN AIR IS USED AS THE OXIDIZING AGENT IN SAID PARTIAL OXIDATION PROCESS, AND ALLOWING SAID HOT GASEOUS MIXTURE TO CONTACT SAID FLUIDIZED BED WHEREBY FURTHER CONVERSION OF SAID OXYGENATED HYDROCARBONS IS HALTED WHILE HYDROCARBONS AND ADDITIONAL OXYGENATED COMPOUNDS ARE BEING INDEPENDENTLY SYNTHESIZED IN SAID ZONE UNDER SAID KNOW CONDITIONS. 